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Old 10th March 2012, 01:39 PM   #1
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Location: Coventry
Default Choosing power supplies for my L25d 8 channel amp.

Hi guys.

I am currently building a fully active three way plus stereo sub system. This is my first real DIY audio adventure and quite a large undertaking – but I am learning a lot and loving it as a new hobby (it’s winter and rolling around under my car isn’t as much fun in the rain and cold!).

I have a MiniDSP 2x8 which will be acting as the pre-amp/crossover/EQ/time-alignment in the audio chain. I have also just ordered a Dayton EMM-6 calibrated mic to use with a newly purchased E-Mu 0404 USB sound card for measurement of room/speakers etc.

The speakers will have the following drivers:

Tweeters: SB Acoustics SB29RDNC-C000-4 [4 ohm neo ring radiator]
Mids: SB Acoustics SB15NRXC30-4 [4 ohm 5”]
Woofers: SB Acoustics SB29NRX75-6 [6 ohm 10”]
Subs: Peerless XLS [8 ohm 10” with 10” 400g passive radiators]

To power these I will need 8 channels of amplification. I originally started looking at HifimeDIY amps about a year ago because of the price and ease of use. I wanted to just plug a meanwell into them and get going. Now I have been lurking enough and reading up on matters I am braver and more proficient with a soldering iron I decided that I would like a kit so I can hand on heart say to people: I made this!

To this end I ordered 4 stereo pairs of ljm_ljm’s L25d. Why the L25d? Because I have only read good things about their sound quality, noise floor, distortion etc etc. Also because they can provide the sub-woofers power handling of 250w into 8 ohm when given high voltage, but have the current capability to drive my 4/6 ohm woofers when used with lower supply voltages. This makes the finished boards more flexible in the long run. It also means (hopefully) that I will be able to scale the power by selecting the power supply for each driver. Obviously the amps are capable of WAY over-powering the drivers but I think that a little self control with the volume knob and lots of extra head-room in terms of power can only be a good thing! I know I have ordered a LOT of power for the mids and tweeters but hope I can scale back by selecting lower voltage supplies and reduce the heat/distortion that comes from the high voltage supplies.

So: onto my question: Can you please help me choose power supplies for my amps? I am basically decided on Connexelectronics regulated SMPS line, but need to choose which exact ones are most suitable for my application.

I am thinking about an SMPS 800R at 70 volts for the sub-woofer amps, an SMPS 500R (voltage undecided) for the [6 ohm 200 watt handling] woofers and a shared SMPS 500 R (voltage un-decided) to power the boards for the tweeters and mids. Later on I could upgrade by buying an SMPS 300R for the tweeter amps maybe?

Can you please talk me through the descision process and choose the right power supplies?

Many thanks for taking the time to read this and I look forward to everyone’s input.

Kind regards,

Jai Stanley
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Old 10th March 2012, 06:10 PM   #2
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Location: Mountain View, CA
Be aware that the L25 has a higher minimum suitable voltage than the L20D and L15D, though I believe you can change some resistors to make them suitable for lower voltage.
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Old 10th March 2012, 08:15 PM   #3
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Hi Jai,
I'd start with an SMPS for the subwoofers, and just one SMPS for the three-way (most power is required for the woofer).
IMO it does not make much sense to cut power for a mid-high; the amps will not clip during normal use (hard clipping is mostly responsible for blown mids and tweeters).
When not satisfied you might add power supplies, but with one power supply and some additional capacitive decoupling for every amp board you might easily get there.
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Old 10th March 2012, 10:13 PM   #4
norazmi is offline norazmi  Malaysia
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8 channel? can u get 2KVA psu? hehe
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Old 10th March 2012, 10:50 PM   #5
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As said, the mids and tweeters will not place big demand on PS compared to woofers and subs.
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Old 11th March 2012, 02:51 PM   #6
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Thank you for the replies. I am beginning to get a better picture of my requirements..

I sat and re-read the L20D thread last night. It appears I need to change a few resistors on the board according tho the IRAudio reference design in order to change the min/max voltage of the amp. I had previously assumed that as LJM didn't include under/over voltage protection in the amp, I could just use a lower supply voltage without doing anything else. Also, the L25D differs from the L15d/L20d in that it isn't an exact implementation of the IRS design. I would need to cross reference the IRS design with the reverse engineering other forum members have already done.

So I have two options:
1: Change these resistors and go with the power supplies I mentioned before.
2: Use the higher supply voltages and not worry about the power output.

As I mentioned I am not too worried about having too much power for my mids and tweeters. Just because an amp CAN supply too much power, I would run out of power to the woofers first and turn the volume down. My car has 320 horse-power and yet I am perfectly able to drive to the shops at 30 mph!

So: Am I right in the following thinking:

I should go for a high voltage amp to drive my subs as they are 8 ohm. This will mean the amp has to dissipate lots of heat and I should probably put larger heat-sinks on them. Possibly put them into a Hifi2000 case with heat-sinks and use copper slugs/heat-pipes to take the heat to the large sinks on the side of the case?

For the 4 ohm Mids and tweeters, and probably the 6 ohm woofers, I will need more current. From what I can gather the L25D will perform better and produce more power and less distortion into these with the lower voltage power supply. To this end I would need a PSU capable of supplying a lot of current.

So:

An SMPS800R +/- 72v, 230VAC, 12V acc for the subs.
An SMPS2000R +/- 60v, 230VAC, 12V acc for everything else.

Comes to $290 plus shipping.

How About:

An SMPS800R +/- 72v, 230VAC, 12V acc for the subs.
An SMPS800R +/- 60v (adjusted to 66v), 230VAC, 12V acc for the Woofers.
An SMPS800R +/- 60v, 230VAC, 12V acc for the Tweeters and Mids.

Comes to $300 plus shipping, so no real difference.


Will I be better off with more supplies to take the strain of the woofers from the power supply for the higher frequency amps?

Would I have noise/supply issues running four channels from one power supply? Would I need capacitive de-coupling that was mentioned, and how do I sec that?

Thank you all for your help!

Perhaps Christi could comment as I am reasonably confident I will be placing an order there soon.

Kind regards,

Jai Stanley
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Old 11th March 2012, 02:56 PM   #7
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Another option would be to power them all with a single SMPS3K6QR. It is capable of supplying +/- 75v at 24A.

Is this enough/too much? Would I suffer problems with heat in a single (quite large) case running all the amps at this voltage?

Kind regards,

Jai
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Old 11th March 2012, 08:00 PM   #8
norazmi is offline norazmi  Malaysia
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Peerless XLS 10" Passive Radiator (830481)

Parameter Value
Fs 13.7 Hz
Qms 11.4
Vas 80 l
Rms 2 Kg/s
Mms 265g
Cms 0.508 mm/N
Sd 333 cm2
xmax 22 mm

i would like to suggest SMPS800R with L25D for the sub. as for the speaker 8 ohm, amp will not produce too much heat i think, because amp running in class D mode. I have with me Iraudump 7D original from international rectifier also run with irs2092 chips. They sound good. mosfet output not produce much heat, but aux supply for +12v will produce more heat than mosfet.

and smps1kw + 2 L15D for the woofer + mid and Tweeter.

we should not choose amp rated more than 70% of the speaker power rms. can cause damage to the speaker . This is my suggestion only i think its enough power for them.
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Old 11th March 2012, 09:18 PM   #9
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Quote:
Originally Posted by jaistanley View Post
For the 4 ohm Mids and tweeters, and probably the 6 ohm woofers, I will need more current.
I can't imagine the mids/tweets demanding the current; as you said the woofers and/or their amps will run out of gas sooner.

And if that current were to flow in the mids/tweets it would fry them in short order.
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Old 11th March 2012, 10:50 PM   #10
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My personal opinion is to drive all channels equally with identical supplies to isolate the pairs from noise and possible damage. Probably not the cheapest solution either, sorry. Might get a price break though. If one large SMPS bit the dust, it could smoke the entire setup. Not to mention smaller SMPS's keep them each loaded in the higher effieciency zone.

I would prefer to make something with equal capabilities across the board, even if you don't need it. Imagine an emotiva / outlaw amp or other brand that had 8 channels of different nameplate powers? They don't really exist. I am the kind to pay extra today for what I might need tommorrow. This is my opinion.

I would do either the 800R or 600R's across the board for each pair. I would make a remote adjustment of the SMPS output voltage for each, kind of like a gain knob for the SMPS. Also install manual volume knobs to limit each output too. You are doing it all digitally, in my past experience with my PC, weird crap happens with the audio when codecs do not work resulting in loud noise / static. Without limits in place it can destroy speakers.

Last edited by NissanSR20Man; 11th March 2012 at 10:53 PM.
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